Field of the Invention
The present invention relates generally to optical fiber devices and methods, and in particular to improved optical fiber winding structures and techniques.
Background Art
There is an ever increasing need for fiber-based optical devices that are compact and use space as efficiently as possible. However, achieving small form factors for fiber-based devices has proven to be problematic. Fiber-based devices commonly include relatively long segments of optical fiber that are wound into coils. At the tighter coil diameters required for smaller form factors, differential group delay (DGD) and polarization mode dispersion (PMD) become increasingly significant.
Generally speaking, a bent fiber has an induced linear birefringence that is inversely proportional to the square of the bending diameter. Thus, in a tight fiber coil, which has a very small bending diameter, the total birefringence is dominated by bend-induced birefringence, irrespective of the fiber's intrinsic birefringence properties. A large bend-induced birefringence results in undesirable amounts of DGD and PMD.
There is thus a need for fiber winding techniques and structures that reduce or eliminate bend-induced birefringence and the resulting DGD and PMD.